This invention relates to semiconductor devices and to the fabrication thereof, and particularly to semiconductor devices having terminal leads of copper.
One type of semiconductor device with which the present invention has utility is shown in U.S. Pat. No. 3,996,602, the subject matter of which is incorporated herein by reference.
This patent shows a semiconductor chip which is brazed between two molybdenum blocks and a pair of copper terminal leads brazed to respective ones of the blocks. The leads are co-axial, and extend in opposite directions from the molybdenum blocks.
In the assembly of the device, the chip, blocks and terminal leads are simultaneously brazed in a batch processing step in which a plurality of assembled devices are passed through a heating oven.
Copper is used for the terminal leads because of the high electrical and thermal conductivities thereof. The copper leads, which may comprise simple lengths of straight wire or leads of the "nail-head" type, i.e., having a radial flange at the ends brazed to the molybdenum blocks, are formed by known cold working methods including drawing the copper wire through a die. Such cold working, as known, tends to stiffen the normally relatively soft copper leads. However, during the batch brazing process, the copper leads are heated to a temperature, e.g., around 700 degrees Cent., which is sufficiently high to cause annealing and softening of the copper leads. The leads are thus easily bent which leads to numerous problems such as lead entanglement when the devices are bulk handled, and the need to straighten the leads for device testing and assembly into end use equipment.
Solutions in the past to the problems associated with soft terminal leads have generally relied upon more careful handling, and in some instances, individual rather than bulk processing and transporting of the devices. Such solutions are undesirable as increasing the cost of the devices.